Force detector and acceleration detector and method of manufacturing the same

ABSTRACT

An electrode layer is formed on the upper surface of a first substrate, and a processing for partially removing the substrate is carried out in order to allow the substrate to have flexibility. To the lower surface of the first substrate, a second substrate is connected. Then, by cutting the second substrate, a working body and a pedestal are formed. On the other hand, a groove is formed on a third substrate. An electrode layer is formed on the bottom surface of the groove. The third substrate is connected to the first substrate so that both the electrodes face to each other with a predetermined spacing therebetween. Finally, the first, second and third substrates are cut off every respective unit regions to form independent sensors, respectively. When an acceleration is exerted on the working body, the first substrate bends. As a result, the distance between both the electrodes changes. Thus, an acceleration exerted is detected by changes in an electrostatic capacitance between both the electrodes.

This is a divisional of application(s) Ser. No. 08/647,178 filed May 9,1996 (now U.S. Pat. No. 5,639,973) which is divisional of applicationSer. No. 08/394,310 filed Feb. 24, 1995 (now U.S. Pat. No. 5,531,002)which is a divisional of application Ser. No. 08/292,496 filed Aug. 18,1994 (now U.S. Pat. No. 5,406,848) which is a divisional of applicationSer. No. 07/764,159 filed Sep. 20, 1991 (now U.S. Pat. No. 5,421,213).

BACKGROUND OF THE INVENTION

This invention relates to a force detector and an acceleration detectorto which the force detector is applied, and more particularly to adetector suitable for detection of multidimensional force oracceleration components. Further, this invention provides a methodsuitable for mass producing such detectors.

In the automobile industry or the machinery industry, there has beenincreased demand for detectors capable of precisely detecting a physicalquantity such as force, acceleration or magnetism. Particularly, it isrequired to realize small detectors capable of detecting physicalquantities every respective two-dimensional or three-dimensionalcomponents.

To meet such a demand, there has been proposed a force detector in whichgauge resistors are formed on a semiconductor substrate such as silicon,etc. to transform a mechanical distortion produced in the substrate onthe basis of a force applied from the external to an electric signal bymaking use of the piezo resistive effect. When a weight body is attachedto the detecting unit of the force detector, an acceleration detectorfor detecting, as a force, an acceleration applied to the weight bodycan be realized. Further, when a magnetic body is attached to thedetecting unit of the force detector, a magnetic detector for detecting,as a force, a magnetism exerted on the magnetic body can be realized.

For example, in U.S. Pat. No. 4,905,523, U.S. Pat. No. 4,967,605, U.S.Pat. No. 4,969,366, U.S. patent application Ser. No. 07/362,399, No.07/470,102, and No. 07/559,381, force detectors using gauge resistor,acceleration detectors, and magnetic detectors are disclosed. Further,in U.S. patent application Ser. No. 07/526,837, a manufacturing methodsuitable for these detectors is disclosed.

Since there generally exists temperature dependency in the gaugeresistance or the piezo resistive coefficient, in the case of the abovedescribed detectors, if there occurs any change in the temperature ofthe environment where those detectors are used, a detected value wouldinclude an error. Accordingly, it is required for carrying out a precisemeasurement to conduct temperature compensation. Particularly, in thecase where such detectors are used in the field of automotive vehicle,etc., temperature compensation is required over the considerably broadoperating temperature range of -40° to +12° C..

In addition, in order to manufacture the above described detectors, ahigh level process for processing the semiconductor substrate isrequired, and a high cost apparatus such as an ion implanter is alsorequired. For this reason, there is the problem that the manufacturingcost becomes high.

SUMMARY OF THE INVENTION

A first object of this invention is to provide a novel detector whichcan detect a physical quantity such as force, acceleration or magnetism,etc. without carrying out temperature compensation, and can be suppliedat a low cost.

A second object of this invention is to provide a manufacturing methodsuitable for mass production of such a novel detector.

1. Feature relating to the detector

To attain the above described first object, the detector according tothis invention is featured as follows:

(1) The first feature resides in a force detector comprising:

a flexible i.e. displacement substrate including a fixed portion fixedto a detector casing, a working portion to which a force from theexternal is transmitted, and a flexible portion having flexibilityformed between the fixed portion and the working portion,

a fixed substrate fixed on the detector casing so as to face theflexible substrate,

a working body adapted to receive a force from the external to transmitthis force to the working portion of the flexible substrate,

a displacement electrode formed on the surface facing to the fixedsubstrate of the flexible substrate, and

a fixed electrode formed on the surface facing to the flexible substrateof the fixed substrate,

wherein any one of the displacement electrode and the fixed electrode,or both the electrodes are constituted by a plurality of electricallyindependent localized electrodes to form a plurality of capacitanceelements by electrodes opposite to each other to detect a force exertedon the working body every multidimensional respective components on thebasis of changes in the electrostatic capacitance values of therespective capacitance elements.

In the force detector having the above mentioned first feature, when aforce from the external is applied to the working body, the flexiblesubstrate bends, so a distance between the displacement electrode andthe fixed electrode varies. Accordingly, an electrostatic capacitancebetween both electrodes varies. Because the change of the electrostaticcapacitance is dependent upon a force applied from the external,detection of force can be made by detecting the change of theelectrostatic capacitance. In addition, at least one of the displacementelectrode and the fixed electrode is constituted by a plurality oflocalized electrodes. A change of an electrostatic capacitance of acapacitance element formed by a localized electrode is dependent upon adirection of a force exerted and a position of the local electrode.Accordingly, changes in electrostatic capacitance values of a pluralityof capacitance elements formed by a plurality of localized electrodesinclude information relating to a direction of the force exerted. Thus,the force exerted can be detected every multidimensional respectivecomponents.

(2) In the force detector having the above desribed first feature, thesecond feature resides in a force detector,

wherein any one of the displacement electrode and the fixed electrode,or both the electrodes are constituted by four groups of localizedelectrodes arranged in positive and negative directions of a first axisand a second axis perpendicular to each other on the surface where thelocalized electrodes are formed (hereinafter referred to as theelectrode formation surface), thus to form four groups of capacitanceelements by using the four groups of localized electrodes, respectively,

a force component in the first axis direction being detected by adifference between electrostatic capacitance values of capacitanceelements belonging to the two groups of capacitance elements on thefirst axis of the four groups of capacitance elements,

a force component in the second axis direction being detected by adifference between electrostatic capacitance values of capacitanceelements belonging to the two groups of capacitance elements on thesecond axis of the four groups of capacitance elements.

In the force detector having the above described second feature, fourgroups of localized electrodes are formed. When the electrode formationsurface is defined as an XY plane, respective groups are formed on theboth positive and negative sides of the X-axis and on the positive andnegative sides of the Y-axis, respectively. When a force in the X-axisdirection is exerted on the working body, since the electrostaticcapacitance values with respect to the both groups positioned on thepositive and negative sides of the X-axis complementarily changes, it ispossible to detect a force in the X-axis direction by the differencebetween electrostatic capacitance values with respect to the bothgroups. Similarly, by the difference between electrostatic capacitancevalues with respect to the both groups positioned on the positive andnegative sides of the Y-axis, it is possible to detect a force in theY-axis direction.

(3) In the force detector having the above described first feature, thethird feature resides in a force detector,

wherein anyone of the displacement electrode and the fixed electrode orboth the electrodes are constituted by four groups of localizedelectrodes arranged in positive and negative directions with respect toa first axis and a second axis perpendicular to each other on theelectrode formation surface to form four groups of capacitance elementsby using four groups of localized electrodes, respectively,

a force component in the first axis direction being detected by adifference between electrostatic capacitance values of capacitanceelements belonging to two groups of capacitance elements on the firstaxis of the four groups of capacitance elements,

a force component in the second axis direction being detected by adifference between electrostatic capacitance values of capacitanceelements belonging to two groups of capacitance elements on the secondaxis of the four groups of capacitance elements,

a force component in the third axis direction perpendicular to the firstaxis and the second axis being detected by a sum of electrostaticcapacitance values of capacitance elements belonging to four groups ofcapacitance elements.

In the force detector having the third feature, four groups of localizedelectrodes are formed. When the electrode formation surface is definedas an XY-plane, respective groups are formed on both the positive andnegative sides of the X-axis and on both the positive and negative sidesof the Y-axis. When a force in the X-axis direction is exerted on theworking body, since the electrostatic capacitance values with respect toboth the groups positioned on the positive and negative sides of theX-axis complementarily vary, it is possible to detect a force in theX-axis direction by the differences between electrostatic capacitancevalues with respect to the both groups. Similarly, it is possible todetect a force in the Y-axis direction by the differences betweenelectrostatic capacitance values with respect to both the groupspositioned on the positive and negative sides of the Y-axis. Inaddition, when a force in the Z-axis direction is exerted on the workingbody, since the electrostatic capacitance values with respect to thefour groups vary in the same direction, it is possible to detect a forcein the Z-axis direction by the sum thereof.

(4) In the force detector having the above described first feature, thefourth feature resides in a force detector,

wherein any one of the displacement electrode and the fixed electrode,or both the electrodes are constituted by four groups of localizedelectrodes respectively arranged in positive and negative directionswith respect to a first axis and a second axis perpendicular to eachother on the electrode formation surface, and a fifth group of localizedelectrodes arranged at the intersecting point of the first axis and thesecond axis to form five groups of capacitance elements by using fivegroups of localized electrodes, respectively,

a force component in the first axis direction being detected by adifference between electrostatic capacitance values of capacitanceelements belonging to two groups of capacitance elements on the firstaxis of the five groups of capacitance elements,

a force component in the second axis direction being detected by adifference between electrostatic capacitance values of capacitanceelements belonging to two groups of capacitance elements on the secondaxis of the five groups of capacitance elements,

a force component in a third axis perpendicular to the first axis andthe second axis being detected by electrostatic capacitance values ofcapacitance elements using the fifth group of localized electrodes ofthe five groups of capacitance elements.

In the force detector having the fourth feature, since an exclusivecapacitance element for detecting a force component in the third axisdirection is formed, more accurate detected values can be provided.

(5) In the force detector having the above described first feature, thefifth feature resides in that the displacement electrode is formed atthe working portion.

In the force detector having the fifth feature, since the displacementelectrode is efficiently subjected to displacement, the sensitivity canbe improved.

(6) In the force detector having the above described first feature, thesixth feature resides in a force detector,

wherein there is further provided an auxiliary substrate so that thefixed substrate, the flexible substrate and the auxiliary substrate areoppositely arranged in order recited, respectively,

wherein a first auxiliary electrode is formed on the surface facing tothe auxiliary substrate of the flexible substrate,

wherein a second auxiliary electrode is formed on the surface facing tothe flexible substrate of the auxiliary substrate, and

wherein a predetermined voltage is applied across the first auxiliaryelectrode and the second auxiliary electrode, or across the displacementelectrode and the fixed electrode to allow the flexible substrate toproduce displacement by a coulomb force exerted therebetween, thuspermitting the force detector to be placed in the state equivalent tothe state where a force is exerted thereon from the external.

In the force detector having the sixth feature, when a predeterminedvoltage is applied across respective electrodes, the flexible substrateis permitted to produce displacement by coulomb force exertedtherebetween. Namely, the force detector can be place in the stateequivalent to the state where a force is exerted thereon from theexternal. If such a state can be created, it becomes easy to test as towhether or not the detector normarily operates.

(7) In the force detector having the above described sixth feature, theseventh feature resides in a force detector,

wherein the flexible substrate is constituted with a conductivematerial, and the first auxiliary electrode and the displacementelectrode are formed by a portion of the conductive flexible substrate.

In the force detector having the seventh feature, the first auxiliaryelectrode and the displacement electrode are formed by a portion of theflexible substrate. Accordingly, the process step for newly forming theelectrode is not particularly required. Thus, the structure becomessimple and the manufacturing cost can be reduced.

(8) The eighth feature resides in a force detector comprising:

a flexible substrate including a fixed portion fixed to a detectorcasing, a working portion to which a force is transmitted from theexternal, and a flexible portion having flexibility formed between thefixed portion and the working portion,

a fixed substrate fixed on the detector casing so as to face theflexible substrate,

a working body adapted to receive a force from the external to transmitthis force to the working portion of the flexible substrate,

a displacement electrode formed on the surface facing to the fixedsubstrate of the flexible substrate,

a fixed electrode formed on the surface facing to the flexible substrateof the fixed substrate, and

a piezo electric element formed in a manner that it is put between thedisplacement electrode and the fixed electrode to transform an appliedpressure to an electric signal by both the electrodes to output it toboth the electrodes,

to detect a force exerted on the working body by an electric signaloutputted from the pizeo electric element.

In the force detector having the eighth feature, when a force from theexternal is applied to the working body, the flexible substrate is bent.Thus, a pressure is applied to the piezo electric element put betweenthe displacement electrode and the fixed electrode. Since this pressureis outputted as an electric signal, an external force can be detected asan electric signal as it is.

(9) In the force detector having the above described eighth feature, theninth feature resides in a force detector wherein a plurality ofdisplacement electrodes are formed on one surface of the piezo electricelement and a plurality of fixed electrodes are formed on the othersurface, thus to detect a force exerted on the working body every pluraldirectional components by electric signals obtained from the pluralityof electrodes.

In the force detector having the ninth feature, it is possible to detectforce components in plural directions by using a single piezo electricelement.

(10) In the detectors having the above described first to ninthfeatures, the tenth feature resides in a detector wherein the workingbody is constituted with a magnetic material to detect a force producedon the basis of a magnetic force exerted on the working body, therebymaking it possible to carry out detection of magnetism.

2. Feature relating to the manufacturing method

To attain the above-described second object, the manufacturing methodaccording to this invention has the following features.

(1) In a method of manufacturing a physical quantity detector utilizingchanges in an electrostatic capacitance, the first feature resides in amethod comprising the steps of:

defining a working region, a flexible region adjacent to the workingregion, and a fixed region adjacent to the flexible region at a firstsubstrate,

forming a first electrode layer on a first surface of the firstsubstrate,

carrying out a processing for partially removing the first substrate inorder to allow the flexible region to have flexibility,

connecting a first surface of a second substrate to a second surface ofthe first substrate,

cutting the second substrate to thereby form a working body connected tothe working region of the first substrate and comprised of a portion ofthe second substrate, and a pedestal connected to the fixed region ofthe first substrate and comprised of a portion of the second substrate,and

forming a groove on a first surface of a third substrate to form asecond electrode layer on the bottom surface of the groove to connectthe third substrate to the first substrate so that the second electrodelayer faces to the first electrode layer with a predetermined spacingtherebetween.

In accordance with the manufacturing method having the first feature, aweight body or a magnetic body (these members are generically called aworking body in this application) are formed by a portion of the secondsubstrate, and a pedestal for supporting the first substrate is formedby another portion thereof. Namely, by cutting the second substrate,both the working body and the pedestal can be formed, so the physicalquantity detector can be efficiently manufactured.

(2) In a method of manufacturing a physical quantity detector utilizingchanges in an electrostatic capacitance, the second feature resides in amethod comprising the steps of:

defining a working region, a flexible region adjacent to the workingregion, and a fixed region adjacent to the flexible region at a firstsubstrate,

forming a first electrode layer on a first surface of the firstsubstrate,

carrying out a processing for partially removing the first substrate inorder to allow the flexible region to have flexibility,

connecting a first surface of a second substrate to a second surface ofthe first substrate,

cutting the second substrate to thereby form a working body connected tothe working region of the first substrate and comprised of a portion ofthe second substrate, and a pedestal connected to the fixed region ofthe first substrate and comprised of a portion of the second substrate,

forming, on a first surface of a third substrate, a groove such that theworking body can move with a predetermined degree of freedom, thereafterto connect the first surface of the third substrate to a second surfaceof the second substrate, and

forming a groove on a first surface of a fourth substrate to form asecond electrode layer on the bottom surface of the groove to connectthe fourth substrate to the first substrate so that the second electrodelayer faces to the first electrode layer with a predetermined spacingtherebetween.

In accordance with the manufacturing method having the second feature, acontrol member for limiting movement in a lower direction of the workingbody can be formed by a different substrate.

(3) In a method of manufacturing a physical quantity detector utilizingchanges in an electrostatic capacitance, the third feature resides in amethod comprising the steps of:

defining a working region, a flexible region adjacent to the workingregion, and a fixed region adjacent to the flexible region at a firstsubstrate,

forming a first electrode layer on a first surface of the firstsubstrate,

carrying out a processing for partially removing the first substrate inorder to allow the flexible region to have flexibility,

forming, on a first surface of a second substrate, a groove such thatthe working region can move with a predetermined degree of freedom,thereafter to connect the first surface of the second substrate to asecond surface of the first substrate,

forming a groove on a first surface of a third substrate to form asecond electrode layer on the bottom surface of the groove to connectthe third substrate to the first substrate so that the second electrodelayer faces to the first electrode layer with a predetermined spacingtherebetween.

As compared to the manufacturing method having the previously describedsecond feature, the manufacturing method having the third featurebecomes more simple.

(4) In the manufacturing methods having the above described first tothird features, the fourth feature resides in a method in which aplurality of unit regions are defined on respective substrates to formsingle independent detectors every unit regions to finally separate themevery respective unit regions.

In accordance with the manufacturing method having the fourth feature,it is possible to mass produce respective detectors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross sectional view showing the structure of anacceleration detector according to a basic embodiment of this invention.

FIG. 2 is a bottom view of the fixed substrate in the detector shown inFIG. 1.

FIG. 3 is a top view of the flexible substrate in the detector shown inFIG. 1.

FIG. 4 is a side cross sectional view showing the state where a force Fxin an X-axis direction is exerted on the detector shown in FIG. 1.

FIG. 5 is a side cross sectional view showing the state where a force Fzin a Z-axis direction is exerted on the detector shown in FIG. 1.

FIG. 6 is a Table showing the principle of the force detection in thedetector shown in FIG. 1.

FIG. 7 is a circuit diagram showing a detection circuit to be applied tothe detector shown in FIG. 1.

FIG. 8 is a cross sectional view showing the embodiment where respectivesubstrates in the detector shown in FIG. 1 are constituted with metalmaterial.

FIG. 9 is a cross sectional view showing the embodiment where respectivesubstrates in the detector shown in FIG. 1 are constituted withinsulating material.

FIG. 10 is a cross sectional view showing the embodiment whererespective substrates in the detector shown in FIG. 1 are constitutedwith semiconductor material.

FIG. 11 is a top view of the flexible substrate of an accelerationdetector according to another embodiment of this invention.

FIG. 12 is a circuit diagram showing a detection circuit to be appliedto the detector shown in FIG. 11.

FIG. 13 is a side cross sectional view showing the structure of anacceleration detector according to a further embodiment of thisinvention.

FIG. 14 is a top view showing the flexible substrate in the detectorshown in FIG. 13.

FIG. 15 is a side cross sectional view showing the state where a forceFx in an X-axis direction is exerted on the detector shown in FIG. 13.

FIG. 16 is a side cross sectional view showing the state where a forceFz in an Z-axis direction is exerted on the detector shown in FIG. 13.

FIG. 17 is a circuit diagram showing a detection circuit to be appliedto the detector shown in FIG. 13.

FIG. 18 is a plan view of the flexible substrate of the embodiment whereonly two dimensional detection is carried out.

FIG. 19 is a side cross sectional view showing the structure of anacceleration detector according to the embodiment having a testfunction.

FIG. 20 is a bottom view of the fixed substrate in the detector shown inFIG. 19.

FIG. 21 is a top view of the auxiliary substrate in the detector shownin FIG. 19.

FIG. 22 is a side cross sectional view showing the state where theacceleration detector of the structure shown in FIG. 19 is accommodatedinto an actual detector casing 40.

FIGS. 23a and 23b are side cross sectional views showing the structureof the embodiment using piezo electric element.

FIG. 24 is a side cross sectional view of a force detector havingsubstantially the same structure as that of the acceleration detectorshown in FIG. 22.

FIG. 25 is a view showing the state where unit regions are defined atthe substrate by the manufacturing method according to this invention.

FIG. 26 is a view showing the state where more simple regions aredefined for brevity of explanation.

FIGS. 27a to 27d are process diagrams showing the prestate of the methodof manufacturing an acceleration sensor center portion according to anembodiment of this invention.

FIGS. 28a and 28b are a side cross sectional view and a bottom view ofthe main substrate 100 shown in FIG. 27a.

FIGS. 29a and 29b are a side cross sectional view and a top view of theauxiliary substrate 200 shown in FIG. 27b.

FIGS. 30a and 30b are a side cross sectional view and a top view of thecontrol substrate 300 shown in FIG. 27d.

FIGS. 31a and 31b are a side cross sectional view and a bottom view ofthe supplementary substrate 400 shown in FIG. 32a.

FIGS. 32a to 32c are process diagrams showing the poststage of a methodof manufacturing an acceleration sensor center portion 500 according toan embodiment of this invention.

FIG. 33 is a perspective view showing an acceleration sensor centerportion manufactured by the method shown in FIGS. 32a to 32c.

FIG. 34 is a side cross sectional view showing the state where theacceleration sensor center portion shown in FIG. 33 is accommodated intothe package.

FIG. 35 is a perspective view showing an acceleration sensor centerportion manufactured by the method according to another embodiment ofthis invention.

FIGS. 36a and 36b are a side cross sectional view and a top view of thecontrol substrate 300' used in a method according to the last mentionedembodiment of this invention.

FIGS. 37a and 37b are a side cross sectional view and a bottom view ofthe supplementary substrate 400' used in the method according to thelast mentioned embodiment of this invention.

FIG. 38 is a side cross sectional view of an acceleration detectoraccording to a still further embodiment of this invention.

FIG. 39 is a side cross sectional view of the embodiment where theworking portion 811 of the flexible substrate 810 is used as the weightbody.

FIG. 40 is a side cross sectional view of the embodiment where thedisplacement electrode is formed on the working portion 911.

FIG. 41 is a top view of the flexible substrate 910 in the detector 900shown in FIG. 40.

FIG. 42 is a side cross sectional view showing a different cross sectionof the detector 900 shown in FIG. 40.

FIG. 43 is a bottom view of the fixed substrate 930 in the detector 900shown in FIG. 40.

FIG. 44 is a side cross sectional view of the embodiment where theweight body 941 and the pedestal 942 are added to the detector 900 shownin FIG. 40.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

§1 Basic Embodiment

FIG. 1 is a side cross sectional view showing the structure of anacceleration detector according to a basic embodiment of this invention.This detector comprises, as the major component, a fixed substrate 10, aflexible substrate 20, a working body 30, and a detector casing 40. Thebottom view of the fixed substrate 10 is shown in FIG. 2. The crosssection cut along the X-axis of the fixed substrate 10 in FIG. 2 isshown in FIG. 1. The fixed substrate 10 is formed as a disk shapedsubstrate as shown, and is fixed at the peripheral portion thereof tothe detector casing 40. On the lower surface thereof, a disk shapedfixed electrode 11 is similarly formed. On the other hand, the top viewof the flexible substrate 20 is shown in FIG. 3. The cross section cutalong the X-axis of the flexible substrate in FIG. 3 is shown in FIG. 1.The flexible substrate 20 is also formed as a disk shaped substrate asshown, and is fixed at the peripheral portion thereof to the detectorcasing 40. On the upper surface thereof, quadrunt disk shapeddisplacement electrodes 21 to 24 are formed. The working body 30 iscolumnar as the upper surface thereof is indicated by broken lines inFIG. 3, and is coaxially connected to the lower surface of the flexiblesubstrate 20. The detector casing 40 is cylindrical, and fixes andsupports the peripheral portions of the fixed substrate 10 and theflexible substrate 20.

The fixed substrate 10 and the flexible substrate 20 are arranged with apredetermined spacing therebetween at positions in parallel to eachother. While both substrates are a disk shaped substrate, the fixedsubstrate 10 is a substrate having high rigidity such that bending isdifficult to occur, whereas the flexible substrate 20 is a substratehaving flexibility such that when a force is applied, bending occurs. Itis now assumed that the working point P is defined at the center ofgravity of the working body 30 as shown in FIG. 1, and that the XYZthree-dimensional coordinate system having the working point P as theorigin is defined as shown. Namely, the X-axis is defined in a rightdirection of FIG. 1, the Z-axis is defined in an upper directionthereof, and the Y-axis is defined in a direction perpendicular to theplane surface of paper and extending toward the back side of the planesurface of paper.

Assuming now that the entirety of this detector is mounted, e.g., in anautomotive vehicle, an acceleration will be applied to the working body30 on the basis of running of the automotive vehicle. By thisacceleration, an external force is exerted on the working point P. Inthe state where no force is exerted on the working point P, as shown inFIG. 1, the fixed electrode 11 and the displacement electrodes 21 to 24are maintained in a parallel state with a predetermined spacingtherebetween. However, if a force Fx in the X-axis direction is exertedon the working point P, this force Fx allows the flexible substrate 20to produce a moment force. As a result, as shown in FIG. 4, bending willbe produced in the flexible substrate 20. By this bending, the spacingbetween the displacement electrode 21 and the fixed electrode 11 isincreased, but the spacing between the displacement electrode 23 and thefixed electrode 11 is decreased. When a force exerted on the workingpoisnt P is assumed to be -Fx in an opposite direction, bending havingthe relationship opposite to the above will be produced. On the otherhand, in the case where a force Fy or -Fy in the Y-axis direction isexerted, changes similar to the above are produced in connection withthe spacing between the displacement electrode 22 and the fixedelectrode 11 and the spacing between the displacement electrode 24 andthe fixed electrode 11. Further, in the case where a force Fz in theZ-axis direction is exerted, as shown in FIG. 5, all the displacementelectrodes 21 to 24 become close to the fixed electrode 11. In contrast,in the case where a force -Fz in an opposite direction is exerted, allthe displacement electrodes 21 to 24 are remote from the fixed electrode11.

Here let consider the capacitance elements constituted with respectiveelectrodes. The lower surface of the fixed substrate 10 shown in FIG. 2and the upper surface of the flexible substrate 20 shown in FIG. 3 areopposite to each other. Accordingly, the opposite relationship betweenelectrodes is such that the displacement electrodes 21 to 24 face theopposite portions of the fixed electrode 11, respectively. In otherwords, the fixed electrode 11 serves as a single common electrode,whereas the dispalcement electrodes 21 to 24 serve as localizedelectrodes localized in the quadrant regions, respectively. Although thecommon electrode is provided as the single common electrode, since fourlocalized electrodes are respectively, independent from an electricalpoint of view, four groups of capacitance electrodes can be formed withrespect to the electric characteristic. The capacitance elementsbelonging to the first group are combination of the displacementelectrode 21 arranged in a negative direction of the X-axis and thefixed electrode 11. The capacitance elements belonging to the secondgroup are combination of the displacement electrode 22 arranged in apositive direction of the Y-axis and the fixed electrode 11. Thecapacitance elements belonging to the third group are combination of thedisplacement electrode 23 arranged in a positive direction of the X-axisand the fixed electrode 11. In addition, the capacitance elementsbelonging to the forth group are combination of the displacementelectrode 24 arranged in a negative direction of the Y-axis and thefixed electrode 11. It is now assusmed that the electrostaticcapacitance values of the respective capacitance elements arerepresented by C1, C2, C3 and C4. In the state where no force is exertedon the working point P as shown in FIG. 1, the electrode intervals ofrespective capacitance elements are all kept at the same value, so theelectrostatic capacitance values all take a standard value C0. Namely,the relationship expressed as C1=C2=C3=C4 holds. However, when a forceis exerted on the working point P, as shown in FIG. 4 or 5, so bendingis produced in the flexible substrate 20, the electrode intervals of therespective capacitance elements vary. As a result, their electrostaticcapacitance values become values different from the standard value C0.When it is assumed that an area of an electrode, an electrode intervaland a dielectric constant are represented by S, d and ε, respectively,an electrostatic capacitance C of a capacitance element is generallydetermined by the following equation:

    C=εS/d.

Accordingly, when the electrode interval becomes short, theelectrostatic capacitance C becomes long, while when it becomes large,the electrostatic capacitance C becomes small.

For example, when a force Fx in the X-axis direction is exerted on theworking point P as shown in FIG. 4, since the interval between thedisplacement electrode 21 and the fixed electrode 11 becomes long, therelationship expressed as C1<C0 holds. On the contrary, since theinterval between the displacement electrode 23 and he fixed electrode 11becomes short, the relationship expressed as C3>C0 holds. At this time,since the intervals between displacement electrodes 22 and 24 and thefixed electrode 11 are such that they partially become short, andpartially become long, the both portions are canceled. Thus, therelationship expressed as C2=C4=C0 holds, resulting in no change in theelectrostatic capacitance. On the other hand, when a force Fz in theZ-axis direction is exerted on the working point P as shown in FIG. 5,the intervals between displacement electrodes 21 to 24 and the fixedelectrode 11 all become short. As a result, the relationship expressedas (C1 to C4)>C0 holds. As stated above, the pattern showing howelectrostatic capacitance values of the four groups of capacitanceelements vary in dependency upon the direction of a force exerted.

FIG. 6 is a Table showing the pattern of how electrostatic capacitancevalues of the four groups of capacitance elements vary. In this Table,"0" indicates that there is no change in the electrostatic capacitance(i.e., takes the standard value C0 as it is), "+" indicates that theelectrostatic capacitance is increased, and "-" indicates that theelectrostatic capacitance is decreased. For example, the column of Fx ofFIG. 6 indicates, as shown in FIG. 4, changes in respectiveelectrostatic capacitance values C1 to C4 when a force Fx in the X-axisdirection is exerted on the working point P. In this case, as previouslydescribed, C1 becomes small, C3 becomes large, and C2 and C4 indicate nochange. As stated above, on the basis of the pattern showing howrespective electrostatic capacitance values vary, the direction of aforce exerted can be recognized. Further, by detecting the degree of thechange (i.e., to such an extent that the electrostatic capacitanceincreases, or decreases), the magnitude of a force exterted can berecognized.

The basic circuit for detecting force components exerted everyrespective axial directions is shown in FIG. 7. Converters 51 to 54 areconstituted with circuits for converting electrostatic capacitancevalues C1 to C4 of the capacitance elements to voltage values V1 to V4,respectively. For example, there may be employed a circuit configurationto convert an electrostatic capacitance value C to a frequency value fby using a CR oscillator, etc. thereafter to further convert thefrequency value f to a voltage value V by using a frequency/voltageconverter. As a matter of course, means for directly converting anelectrostatic capacitance value to a voltage value may be employed. Thedifferential amplifier 55 serves to take a difference between voltagevalues V1 and V3 to output it as a component +Fx in the X-axis directionof a force to be detected. As seen with reference to the columns of Fxand -Fx of FIG. 6, the component ±Fx in the X-axis direction isdetermined by taking a difference between C1 and C3. Further, thedifferential amplifier 56 serves to take a difference between voltagevalues V2 and V4 to output it as a component ±Fy in the Y-axis directionof a force to be detected. As seen with reference to the columns of Fyand -Fy, the component ±Fy in the Y-axis direction is determined bytaking a difference between C2 and C4. As stated above, when an approachis employed to determine the components in the X-axis and Y-axisdirections on the basis of difference, influences due to temperature,etc. can be canceled. As a result, good precision detected values can beprovided. Further, the linearity of the detected values is improved. Inaddition, the adder 57 serves to take sum of voltage values V1 to V4 tooutput it as a component ±Fz in the Z-axis direction of a force to bedetected. As seen with reference to the columns of Fz and -Fz of FIG. 6,the component ±Fz in the Z-axis direction is determined by taking sum ofC1 to C4.

On the basis of the principle as mentioned above, predetermined wiringsare implemented to respective electrodes shown in FIGS. 2 and 3 toconstitute a detection circuit as shown in FIG. 7. Thus, a force exertedon the working point P can be detected as electric signals everyrespective components in the three-dimensional axial directions. Namely,an acceleration exerted on the working body 30 can be detected aselectric signals every respective components in the three-dimensionalaxial directions. Since detections of respective components in the axialdirections are exactly independently carried out, interference withother axes does not take place, so precise detection can be made.Further, the temperature dependency of the detected value is to anegligible degree, resulting in no necessity of processing fortemperature compensation. In addition, since the detector can berealized with a simple structure in which electrodes are only formed onthe structure, the manufacturing cost is also low.

It is to be noted that the detection circuit of FIG. 7 is illustrated asan example, and therefore other circuits may be of course employed. Forexample, a CR oscillating circuit may be used to convert anelectrostatic capacitance value to a frequency value to input it to amicroprocessor to determine three-dimensional acceleration components bydigital computation.

§2 Embodiment Showing Materials of Respective Parts

Subsequently, materials of respective parts constituting the abovedescribed force detector will be described. To carry out detection basedon the above described principle, it is sufficient that the followingconditions are satisfied with respect to the materials.

(1) Respective electrodes are comprised of conductive material.

(2) Respective localized electrodes are electrically insulated from eachother.

(3) The flexible substrate is comprised of material having flexibility.

As long as such conditions are satisfied, any material may be used.Here, preferred embodiments using practical material will now bedescribed.

The embodiment shown in FIG. 8 is directed to the example where metal isused in all of the fixed substrate 10a, the flexible substrate 20a, theworking body 30a. The flexible substrate 20a and the working body 30aare integrally formed. Of course, an approach may be employed toindividually prepare these members thereafter to connect them to eachother. The detector casing 40 is formed, e.g., by metal or plastic,etc., and fixes and supports respective substrates by fitting theperipheral portions of respective substrates into the supporting grooves41 formed on the inner surfaces thereof. Since the fixed substrate 10aitself functions as the fixed electrode 11 as it is, there is no need ofseparately forming the fixed electrode 11. Since the flexible substrate20a is comprised of metal, it is impossible to directly form thereondisplacement electrodes 21a to 24a. In view of this, displacementelectrodes 21a to 24a are formed on the flexible substrate 20a throughan insulating layer 25a of material such as glass or ceramic. In thiscase, in order to allow the flexible substrate 20a to have flexibility,it is sufficient that the flexible substrate 20a is caused to be easilydeformed by allowing the flexible substrate to have small thickness, orallowing it to be wave shaped.

The embodiment shown in FIG. 9 is directed to the example where aninsulating body such as glass or ceramic, etc. is used in all of thefixed substrate 10b, the flexible substrate 20b and the working body30b. The flexible substrate 20b and the working body 30b are integrallyformed. The detector casing 40 is formed by metal or plastic, and fixesand supports respective substrates by fitting the peripheral portions ofrespective substrates into suppsorting grooves 41 formed on the innersurfaces thereof. On the lower surface of the fixed substrate 10b, afixed electrode 11b comprised of metal is formed. Further, on the uppersurface of the flexible substrate 20b, displacement electrodes 21b to24b comprised of metal are formed. In order to allow the flexiblesubstrate 20b to have flexibility, the thickness thereof may be causedto be small, or synthetic resin having flexibility may be used in placeof glass or ceramic. Alternatively, through holes may be partiallyprovided in the flexible substrate 20b to allow it to be easilydeformed.

The embodiment shown in FIG. 10 is directed to the example wheresemiconductor such as silicon is used in all of the fixed substrate 10c,the flexible substrate 20c and the working body 30c. The flexiblesubstrate 20c and the working body 30c are integrally formed. Thedetector casing 40 is formed by metal or plastic, and fixes and supportsrespective substrates by fitting the peripheral portions of respectivesubstrates into supporting grooves 41 formed on the inner surfacethereof. The fixed electrode 11c positioned internally on the lowersurface of the fixed substrate 10c and the displacement electrodes 21cto 24c positioned internally on the upper surface of the flexiblesubstrate 20c are formed by diffusing impurity at a high concentration.In order to allow the flexible substrate 20c to have flexibility, thethickness thereof may be caused to be small, or through holes may bepartially provided.

In addition, various embodiments are conceivable. If a silicon substrateis used, the detector may be of more simple structure by making use ofthe etching processing. For example, when an approach is employed toform grooves by etching at the lower surface of the fixed substrate 10cto form electrodes on the bottom surfaces of these grooves, there may beprovided a structure in which the fixed substrate 10c and the flexiblesubstrate 20c are directly connected to each other.

While explanation has been given in connection with the example wheremetal, insulating body and semiconductor body are used as the materialof respective components, combination of such materials may be used asthe respective components.

§3 Embodiment for Detecting Components in Three Axial Directions byIndependent Electrodes

In the previously described basic embodiment, the detection circuit asshown in FIG. 7 was illustrated. In this detection circuit, the samecapacitance elements are used as the capacitance element for detecting±Fx or ±Fy and the capacitance element for detecting ±Fz. In otherwords, by using a single localized electrode for two kinds ofcapacitance elements, components in two axial directions were detected.In the embodiment which will be described below, components in threeaxial directions are detected by exactly independent exclusiveelectrodes. The top view of a flexible substrate 20d used in theembodiment is shown in FIG. 11. As compared to the flexible substrate 20in the basic embodiment shown in FIG. 3, the formation pattern oflocalized electrodes are somewhat complicated. Eight localizedelectrodes in total are formed. The eight localized electrodes areclassified into four groups. The localized electrodes belonging to thefirst group are electrodes 21d and 21e arranged in a negative directionof the X-axis. The localized electrodes belonging to the second groupare electrodes 22d and 22e arranged in a positive direction of theY-axis. The localized electrodes belonging to the third group areelectrodes 23d and 23e arranged in a positive direction of the X-axis.The localized electrodes belonging to the fourth group are electrodes24d and 24e arranged in a negative direction of the Y-axis.

It is now assumed that the electrostatic capacitance values of fourcapacitance elements comprised of combinations of respective fourelectrodes 21d to 24d to which hatching by dots is implemented in FIG.11 and the fixed electrode 11 opposite thereto are respectivelyrepresented, by C1 to C4, and that the electrostatic capacitance valuesof four capacitance elements comprised of combinations of respectivefour electrodes 21e to 24e to which hatching by slanting lines isimplemented and the fixed electrode 11 opposite thereto are respectivelyrepresented by C1' to C4'. With respect to eight capacitance elements, adetection circuit as shown in FIG. 12 is constituted. Here, converters51 to 54 are circuits for converting electrostatic capacitance values C1to C4 to voltages V1 to V4, and differential amplifiers 55 and 56 arecircuits for amplifying and outputting a difference between inputted twovoltage values. In the same manner as in the previously described basicembodiment, the differential amplifiers 55 and 56 output detected valuesof ±Fx and ±Fy, respectively. The feature of this embodiment resides inthat four electrostatic capacitors C1' to C4' are connected in parallelto generate a voltage V5 corresponding to sum of these capacitancevalues by the converter 58 to output it as a detected value of Fz. Whenconsideration of the principle of detection is made in connection withthe localized electrode shown in FIG. 11, ±Fx is detected by theelectrodes 21d and 23d, ±Fy is detected by the electrodes 22d and 24d,and ±Fz is detected by the electrodes 21e, 22e, 23e and 24e. In thisway, components in three axial directions can be detected by individualand independent electrodes.

While there has been illustrated the example where the electrodes 21d to24e are respectively constituted with independent electrodes forconvenience of explanation, as apparent from the circuit diagram of FIG.12, in practice, capacitance elements constituted with electrodes 21e to24e are connected in parallel. Accordingly, these four electrodes may beintegrally formed on the flexible substrate 20d. Further, in the circuitdiagram of FIG. 12, similar detection can be made by the circuit inwhich C1, C2, C3 and C4 are replaced by C1', C2', C3' and C4',respectively.

This embodiment is convenient in the case of adjusting the detectionsensitivities every respective components in the axial directions. Forexample, in FIG. 11, if the areas of the electrodes 21e, 22e, 23e and24e to which hatching by slating lines is implemented of the figure arecaused to be broad, the detection sensitivity in the Z-axis directioncan be increased. Generally in the detector capable of detectingcomponents in three axial directions, it is preferable to make a designso that respective detection sensitivities of three axes aresubstantially equal to each other. In this embodiment, by adjusting thearea ratio between the region where hatching by slanting lines isimplemented and the region where hatching by dot is implemented of FIG.11, respective detection sensitivities of three axes can besubstantially equal to each other.

The cross sectional view of another embodiment of a detector capable ofdetecting components in three axial directions by independent electrodesis shown in FIG. 13. As seen when compared to the basic embodiment shownin FIG. 1, the feature of the embodiment resides in that the flexibleelectrode is constituted by five electrodes. Namely, as seen from thetop view shown in FIG. 14, on the upper surface of the flexiblesubstrate 20f, sector shaped displacement electrodes 21f to 24f and adisk shaped displacement electrode 25f are formed.

The detecting operation by this detector is as follows. Initially, whena force Fx in the X-axis direction is exerted on the working point P,this force Fx allow the flexible substrate 20f to produce a momentforce, so bending will be produced in the flexible substrate 20f asshown in FIG. 15. By this bending, the interval between the displacementelectrode 21f and the fixed electrode 11 is increased, whereas theinterval between the displacement electrode 23f and the fixed electrode11 is decreased. When it is assumed that a force exerted on the workingpoint P is -Fx in an opposite direction, a bending having therelationship opposite to the above will be produced. As stated above,when the force Fx or -Fx is exerted, there occurs changes in theelectrostatic capacitance with respect to the displacement electrodes21f and 23f. By detecting such changes, the force Fx or -Fx can bedetected. At this time, the intervals between respective displacementelectrodes 22f, 24f and 25f and the fixed electrode 11 are partiallyincreased or decreased. However, it can be considered that suchintervals do not change as a whole. On the other hand, in the case wherea force Fy or -Fy in the Y-axis direction is exerted, similar changesare produced only in connection with the interval between thedisplacement electrode 22f and the fixed electrode 11 and the intervalbetween the displacement electrode 24f and the fixed electrode 11.Further, in the case where a force Fz in the Z-axis direction isexerted, as shown in FIG. 16, the interval between the displacementelectrode 25f and the fixed electrode 11 is decreased. In the case wherea force -Fz in the opposite direction is exerted, the intervaltherebetween is increased. At this time, the intervals betweendisplacement electrodes 21f to 24f and the fixed electrode 11 isdecreased or increased wherein the change relating to the displacementelectrode 25f is most conspicuous. Thus, by detecting changes in theelectrostatic capacitance relating to the displacement electrode 25f, itis possible to detect the force Fz or -Fz. In addition, since detectionsin the X-axis and Y-axis directions are carried out on the basis of thedifference, there is no possibility that such detections undergoinfluence with other components in the axial directions.

Actually, acceleration components in respective axial directions aredetected by a detection circuit as shown in FIG. 17. Namely, theelectrostatic capacitance values of capacitance elements C1 to C5respectively comprised of the displacement electrodes 21f to 25f and thefixed electrode 11 are converted to voltage values V1 to V5 by CVconversion circuits 51 to 55, respectively. An acceleration in theX-axis direction is provided on the terminal Tx as a difference voltageobtained by performing calculation of (V1-V3) by a subtracter 55. Anacceleration in the Y-axis direction is provided on the terminal Ty as adifference voltage obtained by performing calculation of (V2-V4) by asubtracter 56. In addition, an acceleration in the Z-axis direction isprovided on the terminal Tz as a voltage V5 as it is.

§4 Embodiment in which the Electrode Formation Pattern is Changed

In the basic embodiment described in the §1, as shown in FIG. 2, thefixed electrode 11 formed on the fixed substrate 10 is constructed as asingle common electrode, and the displacement electrodes formed on theflexible substrate 20 are constructed as four localized electrodes 21 to24. However, this invention is not limited to such a configuration, buta configuration exactly opposite to the above may be employed. Namely,the fixed electrode 11 formed on the fixed substrate 10 is constructedas four localized electrodes, and the displacement electrodes formed onthe flexible substrate 20 are constructed as a single common electrode.Alternatively, four localized electrodes may be formed on the bothsubstrates, respectively. Also in the embodiment using five localizedelectrodes shown in FIG. 13, similar configuration may be employed.Further, the number of localized electrodes formed on a single substrateis not necessarily required to be four or five. For example, eight orsixteen localized electrodes may be formed. Furthermore, as in theflexible substrate 20g shown in FIG. 18, only two localized electrodes21g and 23g may be formed. In this case, detection of the component inthe Y-axis direction cannot be carried out, but detections relating totwo dimensions of the component in the X-axis direction and thecomponent in the Z-axis direction can be made. In addition, in the casewhere only a detection relating to one dimension is carried out, it issufficient that single electrodes are formed on the both substrates,respectively. Further, it is not limited that the electrode is formedcircular or sector shaped, but the electrode may take any form. Inaddition, respective substrates are not necessarily required to be diskshaped.

§5 Embodiment Having Test Function

Generally, in the case of mass producing any detectors to deliver themto the market, the test process is conducted prior to shipping. That is,the work for confirming whether or not the detector normarily carriesout the detecting operation is conducted. Also in the previouslydescribed acceleration detector, it is preferable to carry out a testprior to shipping. In order to test the acceleration detector, anapproach is generally employed to actually apply an acceleration theretoand confirm an electric signal outputted at this time. However, anequipment for producing an acceleration is required for such a test. Asa result, the test system becomes large.

In the embodiment described below, test prior to shipping can be carriedout without using such a large test system. FIG. 19 is a side crosssectional view showing the structure of an acceleration detectoraccording to the embodiment having such a test function. This detectorcomprises, as a main component, a fixed substrate 60, a flexiblesubstrate 70, a working body 75, an auxiliary substrate 80, and adetector casing 40. The bottom view of the fixed substrate 60 is shownin FIG. 20. The cross section cut along the X-axis of the fixedsubstrate 60 of FIG. 20 is shown in FIG. 19. The fixed substrate 60 is adisk shaped metal substrate, and the periphery thereof is fixed to thedetector casing 40. On the lower surface thereof, four quadrant diskshaped fixed electrodes 61 to 64 are formed through an insulating layer65 such as glass, etc. The flexible substrate 70 is a metal disk havingflexibility and its periphery is also fixed onto the detector casing 40.On the lower surface of the flexible substrate 70, a columnar workingbody 75 is coaxially connected. The upper surface of the flexiblesubstrate 70 constitutes a single displacement electrode opposite to thefixed electrodes 61 to 64. The feature of this embodiment resides inthat an auxiliary substrate 80 is further provided. The top view of theauxiliary substrate 80 is shown in FIG. 21. The cross section cut alongthe X-axis of the auxiliary substrate 80 of FIG. 21 is shown in FIG. 19.The auxiliary substrate 80 is, as shown, a disk shaped metal substratehaving a circular through hole formed at the central portion thereof,and its periphery is fixed onto the detector casing 40. As indicated bysingle dotted lines in FIG. 21, the working body 75 is inserted throughthe through hole at the central portion thereof. On the upper surface ofthe auxiliary substrate 80, four auxiliary electrodes 81 to 84 areformed through an insulating layer 85 such as glass. In this example,the lower surface of the flexible substrate 70 constitutes a singleauxiliary electrode opposite to the auxiliary electrodes 81 to 84. Asstated above, the flexible substrate 70 is a metal mass integrallyformed with the working body 75. The upper surface thereof serves as asingle displacement electrode opposite to the fixed electrodes 61 to 64,and the lower surface thereof serves as a single auxiliary electrodeopposite to the auxiliary electrodes 81 to 84.

In accordance with such a configuration, as previously described, by thefixed electrodes 61 to 64 and the displacement electrode oppositethereto (the upper surface of the flexible substrate 70), four sets ofcapacitance elements can be formed. Thus, an acceleration applied to theworking body 75 can be detected on the basis of changes in theseelectrostatic capacitance values. Further, by the auxiliary electrodes81 to 84 and the displacement electrode (the lower surface of theflexible substrate 70), four sets of capacitance elements are formed,thus making it possible to detect an acceleration. The feature of thisdetector resides in that the state equivalent to the state where anacceleration is exerted can be created without actually exerting anacceleration. Namely, when a predetermined voltage is applied acrossrespective electrodes, a coulomb force is exerted therebetween, so theflexible substrate 70 will bend in a predetermined direction. Forexample, in FIG. 19, when voltages having different polarities areapplied to the flexible substrate 70 and the electrode 63, an attractiveforce based on the coulomb force is exerted therebetween. Further, whenvoltages having different polarities are applied to the flexiblesubstrate 70 and the electrode 81, an attractive force based on thecoulomb force is also exerted therebetween. When such an attractiveforce is exerted, even if any force is not actually exerted on theworking body 75, the flexible substrate 70 will be bent in the samemanner as in the case where a force Fx in the X-axis direction as shownin FIG. 4 is exerted. Further, when voltages having the same polarityare applied to the flexible substrate 70 and the electrodes 81 to 84, arepulsive force based on the coulomb force is exerted therebetween. As aresult, even if any force is not actually exerted on the working body75, the flexible substrate 70 will bend in the same manner as in thecase where a force Fz in the Z-axis direction as shown in FIG. 5 isexerted. Thus, by applying voltages having predetermined polarities torespective electrodes, the state equivalent to the state where forces invarious directions are exerted can be created. Accordingly, it ispossible to test the detector without actually applying an accelerationthereto.

Further, the structure in which the auxiliary substrate 80 shown in FIG.19 is added also provides the secondary effect that when an excessiveacceleration is applied, the flexible substrate 70 can be prevented frombeing damaged. While the flexible substrate 70 has flexibility, it maybe damaged when an excessive force is applied thereto. However, inaccordance with the structure shown in FIG. 19, even in the case wherean excessive force is applied, since the displacement of the flexiblesubstrate 70 limitatively fall within a predetermined range, anexcessive displacement which might be damaged is not produced. Namely,in the case where an excessive acceleration is applied in a lateraldirection (in the X-axis or Y-axis direction) in FIG. 19, the sidesurface of the working body 75 comes into contact with the inner surfaceof the through hole of the auxiliary substrate 80. As a result, any moredisplacement is not produced. Further, in the case where an excessiveacceleration is applied in upper and lower directions (in the Z-axisdirection) in FIG. 19, the upper surface or the lower surface of thebent flexible substrate 70 comes into contact with the fixed electrodes61 to 64 or the auxiliary electrodes 81 to 84. As a result, any moredisplacement is not produced.

FIG. 22 is a side cross sectional view showing the state where theacceleration detector of the structure shown in FIG. 19 is accommodatedinto an actual detector casing 40. Respective electrodes and externalterminals 91 to 93 are connected by way of bonding wires 94 to 96(Actually, electrically independent electrodes are respectivelyconnected to exclusive external terminals by way of bonding wires, butonly main wirings are indicated in the figure). The upper surface of thefixed substrate 60 is connected to the internal upper surface of thedetector casing 40, and is firmly held so that the fixed substrate 60does not bend.

§6 Embodiment Utilizing the Piezo Electric Element

In the previously described various embodiments, since an external forcecan be detected as changes in electrostatic capacitance values, aprocessing circuit for converting the electrostatic capacitance value toa voltage value, etc. is required from a practical point of view. In theembodiment shown in FIG. 23a, such a processing circuit becomesunnecessary by making use of the piezo electric element. The basicconfiguration of the detector of this embodiment is common to those ofthe previously described various embodiments. Namely, fixed substrate10h and flexible substrate 20h are affixed within the detector casing 40so that they are opposite to each other. In this embodiment, the bothsubstrates are comprised of an insulating body,. but may be comprised ofmetal or semiconductor. When an external force is exerted on the workingbody 30h, the flexible substrate 20h will bend. As a result, thedistances between the fixed electrodes 11h and 12h and the displacementelectrodes 21h and 22h opposite thereto vary. In the previouslydescribed embodiment, a change of the distance between both theelectrodes is detected as a change of the electrostatic capacitance. Incontrast, in this embodiment, such a change can be detected as a voltagevalue. To realize this, piezo electric elements 45 and 46 are formed sothat they are put between the fixed electrodes 11h and 12h and thedisplacement electrodes 21h and 22h. Of course, an approach may beemployed to form respective electrodes on both the upper and lowersurfaces of the piezo electric elements 45 and 46 thereafter to allowthem to be put between the fixed substrate 10h and the flexiblesubstrate 20h. If the distance between both the electrodes iscontracted, a compressive force is exerted on the piezo electricelements 45 and 46. In contrast, if that distance is expanded, a tensileforce is exerted on the piezo electric elements 45 and 46. As a result,a voltage corresponding to each force is produced by the piezo electriceffect. Since such a voltage can be taken out from both the electrodesas it is, an external force exerted can be eventually outputted directlyas a voltage value.

As the piezo electric elements 45 and 46, for example, PZT ceramics(solid solution of lead titanate and lead zirconate) may be used. Inuse, it is sufficient to mechanically connect this between both theelectrodes. Although only the side cross sectional view is shown in FIG.23a, it is enough for detecting a three dimensional acceleration toarrange four sets of piezo electric elements in the same manner as inthe electrode arrangement shown in FIG. 3. Alternatively, in the samemanner as in the electrode arrangement shown in FIG. 11, eight sets ofpiezo electric elements (four sets of piezo electric elements fordetecting a force in the Z-axis direction of the eight sets thereof canbe substantially combined into one set) may be arranged. Further, inorder to detect a two dimensional acceleration, two sets of piezoelectric elements may be arranged in the same manner as in the electrodearrangement shown in FIG. 18. Also in the case where the detector isaccommodated into the actual detector casing 40, configurationsubstantially similar to that of the embodiment shown in FIG. 22 isprovided. In this case, voltage values are directly outputted fromexternal terminals 91 to 93.

The secondary effect of this embodiment shown in FIG. 23a is that thepiezo electric elements 45 and 46 have a protective function against theflexible substrate 20h. Namely, even in the case where an excessiveforce is applied, since the flexible substrate 20h only bends by theexistence of the piezo electric elements 45 and 46 so that bending doesnot exceed a predetermined limit, there is no possibility that theflexible substrate 20h may be damaged. In addition, in the same manneras in the embodiment having the previously described test function,pseudo test in which a coulomb force is exerted between both theelectrodes can be conducted.

The embodiment shown in FIG. 23b is directed to the example where asingle common piezo electric element 47 is put between the fixedsubstrate 10i and the flexible substrate 20i. Five fixed electrodes 11ito 15i and five displacement electrodes 21i to 25i are formed on theupper surface and the lower surface of the common piezo electric element47 in the same arrangement as in FIG, 14, respectively. In a mannerstated above, only a single common piezo electric element may be used.

§7 Other Embodiments Relating to the Detector

While the detector according to this invention has been described inconnection with several embodiments, it should be noted that thisinvention is not limited only to these embodiments, but may be furthercarried out in various forms. Particularly, in the above describedembodiments, there has been shown the example where this invention isapplied to an acceleration detector for detecting an accelerationapplied to the working body. However, the basic concept of thisinvention resides in the mechanism for detecting a force exerted on thebasis of any physical phenomenon on the working body. Accordingly, it isa matter of course that this invention can be applied to a detector fordirectly detecting a force in place of the acceleration. FIG. 24 is aside cross sectional view of a force detector having substantially thesame structure as that of the acceleration detector shown in FIG. 22. Atthe lower surface of the detector casing 40, a through hole 42 isformed. A contact 76 extending from a working body 75 is insertedthrough the through hole 42. Thus, it is possible to directly detect aforce exerted on the front end portion of the contact 76. Further, inthe acceleration detector shown in FIG. 22, if the working body 75 isformed by magnetic material such as iron, cobalt or nickel, etc., sincea force based on magnetism is exerted on the working body 75 when placedin a magnetic field, it is possible to detect magnetism. Thus, thisinvention can be applied also to the magnetic detector.

As stated above, in accordance with the physical quantity detectoraccording to this invention, since an approach is employed to detect aforce, on the basis of changes in electrostatic capacitance values ofcapacitance elements formed by the displacement electrodes adapted sothat they undergo displacement by force/acceleration/magnetism subjectto detection and the fixed electrodes fixed in a manner oppositethereto, or on the basis of changes in output from piezo electricelements put between both the electrodes, it is possible to realize, ata low cost, a detector capable of detecting a physical quantity such asforce, acceleration, or magnetism, etc. without carrying out temperaturecompensation.

Further, the physical quantity detector according to this invention canbe applied also to a detector using servo system in which feedbackcontrol is carried out by applying an voltage between electrodes tocontrol a distance therebetween with coulomb force so that a capacitanceof a capacitance element or an output voltage of a piezo electricelement becomes constant.

§8 Manufacturing Process I According to This Invention

The configurations of the detector according to this invention have beendescribed in connection with various embodiments. Subsequently, a methodsuitable for manufacturing these detectors will be described. Here,explanation will be given by taking an example of a method ofmanufacturing a detector in which the displacement electrode iscomprised five localized electrodes. The feature of the manufacturingmethod described here resides in that a plurality of sensor units areformed on a single substrate thereafter to carry out cutting everyrespective units (dicing or etching: the example for dicing respectiveunits will be described below). As the manufacturing process I, theprocess up to dicing every respective units will be first described.

Initially, a plurality, of unit regions are defined. A main substrate isseparately cut off every unit regions at the subsequent dicing process.Thus, respective unit regions independently function as displacementsubstrates. FIG. 25 shows a plurality of unit regions formed on the mainsubstrate 100. The portion to which hatching is implemented representsone unit region. Each unit region is square. In the case where wafersuch as semiconductor is used as the main substrate 100, a large numberof unit regions are generally formed on a disk shaped substrate in amanner stated above. However, for convenience of explanation, thefollowing description will proceed by taking the example where four unitregions (the portion to which hatching is implemented is one unitregion) are formed on a square main substrate 100 as shown in FIG. 26.

FIGS. 27a to 27d are cross sectional views showing respective processsteps of this manufacturing method. These process steps will now bedescribed in detail. Initially, the main substrate 100 is processed asshown in FIG. 28. A single crystal silicon substrate is used as the mainsubstrate 100 in this embodiment, but a substrate of other material suchas a glass substrate, etc. may be used. As previously described, themain substrate 100 is square for convenience of explanation, and isdivided into four unit regions. Accordingly, exactly the same processingis implemented to respective four unit regions. FIG. 28b is a bottomview of the processed main substrate 100, and FIG. 28a is a side crosssectional view showing the state cut along the cutting line a--a of themain substrate 100. On the upper surface of the main substrate 100,first electrode layers E1 are formed at predetermined positions. Thesefirst electrode layers E1 correspond to five displacement electrodes 21to 25 shown in FIG. 14 (In FIG. 28a, two units of the cross sections ofthree displacement electrodes thereof are separately shown), and areformed at positions as shown in FIG. 14. In this embodiment, bydiffusing impurities into the surface portion of the main substrate 100comprised of a single crystal silicon substrate, the above mentionedfirst electrode layers E1 are formed. In addition, the first electrodelayers E1 may be formed by using a method of attaching an aluminum layeronto the main substrate 100 through an insulating layer. In short, thefirst electrode layers E1 may be formed by any method capable of forminga conductive layer. The method based on formation of an impuritydiffused layer or formation of an aluminum layer is preferable in thatthe conventional semiconductor planar process can be utilized as it is.On the other hand, grooves 101 are formed at the lower surface of themain substrate 100 by the method such as etching, etc. to cause thethickness of that portion to be thin, thus allowing the main substrate100 to have flexibility. In this embodiment, each groove 101 is circularas shown in FIG. 28b. The inside portion of the groove 101 serves as aworking portion 110, the outside portion thereof serves as a fixedportion 130, and the groove portion serves as a flexible portion 120.Electrode layers corresponding to displacement electrodes 21f to 24fshown in FIG. 14 of the first electrode layers E1 are just formed on theflexible portion 120 above the grooves, and an electrode layercorresponding to the displacement electrode 25f is formed on the workingportion 110 surrounded by each groove. FIG. 27a shows the state whereprocessing of the main substrate 100 is completed.

Subsequently, an auxiliary substrate 200 as shown in FIGS. 29a and 29bis prepared. Since a portion of the auxiliary substrate 200 and theremaining portion thereof constitute a weight body and a pedestal,respectively, material suitable for the weight body and the pedestalshould be used. Further, since the auxiliary substrate 200 is connectedor bonded to the main substrate 100, it is preferable to use a materialhaving substantially the same coefficient of thermal expansion as thatof the main substrate 100. For example, it is preferable to use siliconsubstrate which is the same as the main substrate 100, or glasssubstrate. FIG. 29b is a top view of the processed auxiliary substrate200 and FIG. 29a is a side cross sectional view showing the state wherethe auxiliary substrate 200 is cut along the cutting line a--a. In thisway, grooves 201 and 202 are longitudinally and breadthly formed on theupper surface of the auxiliary substrate 200. The groove 201 is a deepgroove having a width L1, and the groove 202 is a shallow groove havinga width L2. The groove 201 serves to allow the substrate to be easilysubjected to dicing at the subsequent process step. In short, the groove201 is only required to be formed at a position such that portions 210(four portions in the figure) corresponding to the working portion 110of the main substrate 100 and portions 220 (other portions)corresponding to the fixed portion 130 can be separated. In other words,the auxiliary substrate 200 is caused to overlap with the main substrate100, and is connected or bonded thereon. In this case, it is onlyrequired that when solely the auxiliary substrate 200 is cut along thegroove 201, the auxiliary substrate 200 can be separated into the weightbody (portions 210) and the pedestal (portions 220). Further, the groove202 serves to provide degree of freedom relating to displacement in anupper direction of the weight body which has been cut. After such anauxiliary substrate 200 is prepared, this auxiliary substrate isconnected or bonded to the main substrate 100 as shown in FIG. 27b. Thisbonding may be carried out by adhesive agent. However, in order to carryout secure bonding, it is preferable to use the anodic bonding or thedirect bonding capable of directly bonding materials each other. Namely,in case of the anodic bonding, a voltage is applied across the bothmembers to elevate the temperature of both the members to bond themwhile applying a pressure. In case of the direct bonding, it is notneeded to apply a voltage.

Subsequently, as shown in FIG. 27c, the auxiliary substrate 200 is cutalong the groove 201 by means of a dicing blade. Each cutting path 203is formed on the opposite side (lower part in the figure) to the groove201. Thus, the portions 210 (serving as the weight body) and theportions 220 (serving as the pedestal) will be completely cut off. Asshown in FIG. 29b, the portions 210 (weight body) are positioned at fourplaces. Thus, there results the state where such portions are bondedonly to the working portion 110 shown in FIG. 28b. Further, thereresults the state where the remaining portions 220 (pedestal) are bondedonly to the fixed portion 130 shown in FIG. 28b. It is to be noted thatsince the flexible portion 120 is in the state floating from theauxiliary substrate 200, it is not bonded to any portion. As statedabove, by dicing the auxiliary substrate 200, the weight body 210 andthe pedestal 220 can be formed at the same time. Here, the pedestal 220not only performs the function as the pedestal supporting the fixedportion 130, but also performs the control member for conducting acontrol so that the displacement in a lateral direction of the weightbody 210 does not exceed an allowable range. This allowable range willbe determined by the width of the cutting path 203 (In the case wherethe width of the groove 201 is smaller than the width of the cuttingpath 203, the allowable range is determined by the width of the groove201). It is to be noted that the dicing process carried out here is thedicing process for only the auxiliary substrate 200. Accordingly, themain substrate 100 is still in the state of a single substrate.

Subsequently, a control substrate 300 as shown in FIGS. 30a and 30b isprepared. This control substrate 300 serves to control the weight body210 so that displacement in a lower direction thereof falls within anallowable range. As the material of the control substrate 300, siliconsubstrate or glass substrate may be used in the same manner as in theauxiliary substrate 200. Exactly the same processing is implemented tothe upper surface of the control substrate 300 in connection withrespective four units. FIG. 30b is a top view of the processed controlsubstrate 300, and FIG. 30a is a side cross sectional view showing thestate where the control substrate 300 is cut along the cutting linea--a. On the side of the upper surface thereof, square grooves 301 areformed at four portions. These grooves 301 serve to control the degreeof freedom in a lower direction of displacement of the weight body 210wherein the degree of freedom is determined by the depth of the groove301. This control substrate 300 is connected or bonded to the auxiliarysubstrate 200 as shown in FIG. 27d. Also in this bonding, it ispreferable to use the anodic bonding or the direct bonding.

Subsequently, a supplementary substrate 400 as shown in FIGS. 31a and31b is prepared. This supplementary substrate 400 serves to support thesecond electrode layers E2. As the material of the supplementarysubstrate, silicon substrate or glass substrate may be used in the samemanner as in the main substrate 100. Exactly the same processing isimplemented to the lower surface of the supplementary substrate 400 inconnection with respective four unit regtions. FIG. 31b is a bottom viewof the processed supplementary substrate 400, and FIG. 31a is a sidecross sectional view showing the state where the processed supplementarysubstrate 400 is cut along the cutting line a--a. On the lower surfacethereof, square grooves 401 are formed at four portions, and secondelectrode layers E2 are formed on the bottom surfaces of the grooves401, respectively. These second electrode layers E2 correspond to thefixed electrodes 11 shown in FIG. 13, and are formed at positions asshown in FIG. 13, i.e., at positions opposite to the displacementelectrodes 21 to 25. In this embodiment, grooves 401 are formed by theprocess such as etching, etc. on the surface of the supplementarysubstrate 400 comprised of a single silicon substrate thereafter to formsecond electrode layers E2 by the process for attaching an aluminumlayer on the bottom surfaces of these grooves 401 through insulatinglayers. As a matter of course, second electrode layers E2 may be formedby the impurity diffusion process in the same manner as in the firstelectrode layer E1. In short, second electrode layers E2 may be formedby any process capable of forming a layer having conductive property.The process based on formation of the impurity diffused layer orformation of the aluminum layer is preferable in that the technology ofthe conventional semiconductor planar process can be utilized as it is.The formation of the grooves 401 and/or the formation of the secondelectrode layers E2 can be carried out with an extremely high accuracyby making use of the micro machining technology used in thesemiconductor process. Another feature of the supplementary substrate400 resides in that the width in a lateral direction is slightly smallerthan those of other substrates, and that a longitudinally elongatedgroove 402 is formed at the center of the supplementary substrate 400.This is the device for facilitating the wire bonding to be carried outas described later. This supplementary substrate 400 is connected orbonded to the main substrate 100 as shown in FIG. 32a. Also in thisbonding, it is preferable to use the Anodic bonding or the Directbonding. Thus, the first and second electrode layers E1 and E2 areopposite to each other in upper and lower directions of the figure. Itis preferable that the distance between both electrodes is as narrow aspossible from viewpoints of increasing the electrostatic capacitance andcarrying out high sensitivity measurement. By making use of thepreviously described micro machining technology, the distance betweenboth the electrodes can be held down to about several μm.

Thereafter, as shown in FIG. 32b, the upper parts of the groove 402 iscut off by cutting paths 403. Further, when respective unit regions arecut along a cutting path 510 as shown in FIG. 32c, four unit regionsshown in FIG. 26 are separated, respectively. Thus, each sensor centerportion 500 is completed. The perspective of the sensor center portion500 thus completed is shown in FIG. 33. The reason why the width in alateral direction of the supplementary substrate 400 is formed short andthe longitudinally elongated groove 402 is formed is to allow bondingpads 501 to be exposed as shown in FIG. 33.

§9 Manufacturing Process II According to This Invention

Subsequently, the process steps after respective substrates have beensubjected to dicing will be described. If the sensor center portion 500as shown in FIG. 33 is provided, this sensor center portion isaccommodated into a package 600 as shown in the side cross sectionalview of FIG. 34. Namely, this is accomplished by allowing the bottomportion of the sensor center portion 500 to adhere on the internalportion of the package 600. Mounting leads 610 are attached to thepackage 600, and bonding pads 501 and the inside ends of the leads 610are subjected to bonding by bonding wires 620. Thereafter, when a cover636 is fitted over the package 600 and is sealed, an acceleration sensoris completed.

As stated above, as compared to the manufacturing process everysubstrate (the previously described manufacturing process I), themanufacturing process every respective units after dicing (the abovedescribed manufacturing process II) is very simple. Namely, inaccordance with this invention, most of manufacturing process steps canbe carried out every substrate. Thus, an efficient manufacturingsuitable for mass production can be conducted.

§10 Other Embodiments Relating to the Manufacturing Method

While the manufacturing method according to this invention has beendescribed in connection with the embodiment shown, this invention is notlimited to this embodiment, but may be carried out in various forms. Anembodiment in another form will now be illustrated.

(1) While the control substrate 300 is connected or bonded in the abovedescribed embodiment, the fundamental idea of this invention resides inthat the weight body and the pedestal are formed by the auxiliarysubstrate 200. Accordingly, the process for bonding the controlsubstrate 300 is not necessarily required. For example, if the bottomsurface of the weight body 210 is subjected to shaving or similarprocessing so that the thickness of the weight body 210 is slightlysmaller than the thickness of the pedestal 220, the bottom surface ofthe pedestal 220 may be directly connected or bonded to the bottomsurface of the internal portion of the package 600. Since the thicknessof the weight body 210 is slightly smaller than the thickness of thepedestal 220, under the state where no acceleration is exerted, theweight body 210 can be maintained in the state floating from the bottomsurface of the internal portion of the package 600.

(2) While the method of manufacturing an acceleration sensor has beendescribed in the above described embodiment, exactly the same processcan be carried out also in the case of manufacturing a magnetic sensor.It is to be noted that while the working body exerting a force on theworking portion was the weight body 210 in the case of the accelerationsensor, the working body must be a magnetic body in the case of themagnetic sensor. Accordingly, magnetic material is required to be usedas the material of the auxiliary substrate 200.

(3) In the auxiliary substrate 200 shown in FIG. 29, grooves 201 areformed in advance. These grooves serve to facilitate the work forcutting the auxiliary substrate 200 at the subsequent process, andtherefore are not necessarily required. Namely, if the auxiliarysubstrate 200 can be properly cut at the subsequent process, the grooves201 are not required.

(4) In the case of cutting the auxiliary substrate 200 to form a weightbody 210 and a pedestal 220, the auxiliary substrate 200 is cut bydicing in the above described embodiment. In addition, the auxiliarysubstrate 200 may be separated by chemical etching. The term cutting inthis specification includes separation by etching as well.

(5) In the control substrate 300 shown in FIG. 30, square grooves 301are formed every respective unit regions. In place of this, there may beused a control substrate 300' having longitudinally elongated grooves302 formed striding over unit regions as shown in FIGS. 36a and 36b.

(6) In the above described embodiment, as shown in FIG. 33, theelectrical connection between the bonding pads 501 and respectiveelectrode layers (not shown in FIG. 33) is carried out by the diffusedlayers inside the main substrate. However, in the type in which wiringlayers 502 such as aluminum, etc. are formed on the substrate to make anelectrical connection therebetween, as in the sensor center portion 500'shown in FIG. 35, it is necessary to ensure gaps 503 for the wiringlayers 502. In this case, in place of the supplementary substrate 400shown in FIG. 31, a supplementary substrate 400' having grooves 404 asshown in FIGS. 37a and 37b may be used.

(7) While explanation has been given in the above-described embodimentin connection with the example where the square substrate shown in FIG.26 is used to manufacture four sets of sensor center portions forconvenience of explanation, larger number of sensor center portions canbe manufactured by using the disk shaped wafer as shown in FIG. 25 froma practical point of view. As a matter of course, only a set of sensorcenter portions may be manufactured by a single substrate (wafer).

(8) While the space around the weight body 210 is filled with air in theabove-described embodiment, if silicon oil, etc. is sealed into thisspace, impact or vibration absorbing effect is provided, resulting inimproved impact proof and vibration proof.

(9) In order to take out, as a signal, changes in an electrostaticcapacitance, it is generally required to provide an oscillation circuitconnected to capacitance elements, an amplifier circuit for amplifyingan output from the oscillation circuit, and a counter circuit forcounting a frequency of an amplified signal, and the like. If the mainsubstrate 100 is constituted with a semiconductor substrate, the abovementioned circuits can be formed on the main substrate 100.

(10) As shown in FIG. 13, in the embodiment which has been describedare, single fixed electrode 11 is formed on the fixed substrate 10 sideand five displacement electrodes 21 to 25 are formed on the displacementsubstrate 20 side. Conversely, there may be employed an arrangement suchthat five fixed electrodes are formed on the fixed substrate 10 side anda single displacement electrode is formed on the displacement substrate20 side.

(11) Further, in the above described embodiment, one of oppositeelectrode layer is formed with a single electrode layer and the otherelectrode is formed with five electrode layers. In this case, the singleelectrode layer is used as the common electrode from a viewpoint of theconfiguration of the detection circuit. On the contrary, both theelectrodes may be formed with five electrode layers, respectively. Inthis case, five sets of completely independent capacitance elements areconstituted. Thus, detection processing having higher degree of freedomcan be carried out.

(12) While, in the above described embodiment, five displacementelectrodes 21f to 25f are arranged in a form as shown in FIG. 14 todetect acceleration components in three-dimensional directions, anacceleration component in the Z-axis direction can be conducted withoutusing the displacement electrode 25f. Namely, as shown in FIG. 3, onlyfour displacement electrodes 21 to 24 can be used, thus making itpossible to detect acceleration components in three-dimensionaldirections. However, in the case of carrying out good precisionmeasurement in which interference with other axis components issuppressed, five electrode arrangement as shown in FIG. 13 is ideal. Inother words, it is preferable that detection of the component in theZ-axis direction is carried out by the electrode 25f arranged at thecenter thereof and detection of the component in the X-axis or Y-axisdirection is carried out by the electrode 21f to 24f arranged around theelectrode 25f. It can be understood from FIG. 15 that when a forcecomponent in the X-axis or Y-axis direction is exerted, displacement ofthe electrodes 21f to 24f is more conspicuous than displacement of theelectrode 25f (since the electrode 25f is arranged at the centralportion, it can be considered that it undergoes no displacement whenviewed as a whole). Accordingly, it is suitable for detection of thecomponent in the X-axis or Y-axis direction to use electrodes 21f to24f. Further, it can be understood from FIG. 16 that when a forcecomponent in the Z-axis direction is exerted, displacement of theelectrode 25f is more conspicuous than displacement of the electrodes21f to 24f. Accordingly, it is suitable for detection of the componentin the Z-axis direction to use the electrode 25f.

As stated above, in accordance with the manufacturing method accordingto this invention, since an approach is employed to form every substratethe working body (weight body or magnetic body) and the pedestal, and tocarry out every substrate formation of necessary electrode layers,sensors utilizing changes in an electrostatic capacitance can beefficiently mass produced.

§11 Still Further Several Embodiments

Finally, still further several embodiments will be disclosed. FIG. 38 isa side cross sectional view of an acceleration detector 700 according toa still further embodiment. This acceleration detector has therelationship between the weight body and the pedestal which is oppositeto that in the case of the previously described detectors. Namely, theperipheral portion around the flexible substrate 710 serves as a workingportion 711, the central portion thereof serves as a fixed portion 713,and the portion therebetween serves as a flexible portion 712. Theweight body 721 is in the form of doughnut, and is connected or bondedto the lower surface of the working portion 711. The fixed portion 713is supported by a pedestal 722, and the pedestal 722 is fixed on a basesubstrate 730. On the upper surface of the flexible substrate 710, afixed substrate 740 is connected or bonded. Since the fixed substrate isconnected or bonded only at the central portion of the lower surfacethereof to the flexible substrate 710 and grooves are formed at theperipheral portion thereof, the flexible substrate 710 and the fixedsubstrate 740 are maintained with a gap between the upper surface of theflexible substrate 710 and the lower surface of the fixed substrate 740.On the upper surface of the flexible substrate 710, five electrodes 751to 755 (only three electrodes are illustrated in the figure) are formedthrough an insulating film. By these five electrodes 751 to 755 and thefixed substrate 740, five sets of capacitance elements are formed. Thus,ah acceleration exerted on the weight body 721 can be detected.

In the detectors which have been described, there is employed thestructure that the central portion of the flexible substrate serves asthe working portion, the peripheral portion serves as the fixed portion,and the pedestal connected or bonded to the fixed portion surrounds theweight body connected or bonded to the working portion. On the contrary,in the detector 700 shown in FIG. 38, there is employed the structurethat the peripheral portion of the flexible substrate serves as theworking portion, the central portion thereof serves as the fixedportion, and the weight body connected or bonded to the working portionsurrounds the pedestal connected or bonded to the fixed portion. Themanufacturing methods shown in §8 and §9 can be applied also to theacceleration detector of such a structure.

FIG. 39 is a side cross sectional view of an acceleration detector 800of a more simple structure. This acceleration detector is the same asthat of the previously described embodiment in that the central portionof the flexible substrate 810 serves as a working portion 811, theperipheral portion thereof serves as a fixed portion 813, and theportion therebetween serves as a flexible portion 812. However, acontrol substrate 820 is connected or bonded to the lower surface of theflexible substrate 810, and the weight body is not provided. In the samemanner as in the previously described embodiment, a fixed substrate 830is connected or bonded on the upper surface of the flexible substrate810, and five sets of capacitance elements are formed by fivedisplacement electrodes 851 to 855 (only three electrodes areillustrated in the figure) and a fixed electrode 831 to detect anacceleration exerted on the working portion 811. When the structureshown in FIG. 39 is compared, e.g. to the structure of the sensor centerportion 500 shown in FIG. 32c, it can be understood that the structureshown in FIG. 39 is just the structure in which the weight body 210 andthe pedestal 220 constituted by the auxiliary substrate 200 are omitted.Since the auxiliary substrate 200 is unnecessary, the structure becomessimple and the manufacturing process is simplified. Namely, thisstructure is accomplished by connecting or bonding the control substrateshown in FIG. 30a onto the lower surface of the main substrate 100 shownin FIG. 28a, and connecting or bonding the supplementary substrate shownin FIG. 31a onto the upper surface of the main substrate 100. However,since the working portion 811 performs the function as the weight body,the sensitivity is lowered.

While the structure shown in FIG. 39 can be advantageously realized byallowing three substrates to overlap with each other, the sensitivity isdisadvantageously lowered as described above. A detector having astructure capable of compensating this drawback is shown in FIG. 40. Inthis detector 900, the flexible substrate 910 is comprised of a workingportion 911 at the central portion, a fixed portion 913 at theperipheral portion thereof, and a flexible portion 912 providedtherebetween. The area occupation ratio of the working portion 911 ishigh. A control substrate 920 is connected or bonded on the lowersurface of the flexible substrate 910, and a fixed substrate 930 isconnected or bonded on the upper surface thereof. By displacementelectrodes 951 to 955 (only three electrodes are illustrated in FIG. 40)formed on the upper surface of the flexible substrate 910 and the fixedelectrode 931 formed on the lower surface of the fixed substrate 930,five sets of capacitance elements are formed to detect an accelerationexerted on the working portion 911. The feature of this embodiment isclearly shown in FIG. 41. FIG. 41 is a top view of the flexiblesubstrate 910 in the detector shown in FIG. 40. The cross section cutalong the cutting line 40--40 of the flexible substrate 910 is shown inFIG. 40 and the cross section cut along the cutting lines 42--42 isshown in FIG. 42. The remarkable feature of this flexible substrate 910resides in that L shaped through holes 961 to 964 are formed as shown.By these L shaped through holes 961 to 964, the flexible substrate 910is roughly divided into a peripheral frame-shaped fixed portion 913 andan internal square working portion 911. The working portion 911 is inthe state where it is connected to the fixed portion 913 throughflexible portions 912 at four portions. Eventually, four flexibleportions 912 in a beam form support the working portion 911 so as toallow the working portion 911 to hang from four directions. Anotherfeature resides in that displacement electrodes 951 to 955 are allformed on the working portion 911. As shown in FIG. 43, a fixedelectrode 931 is formed on the lower surface of the fixed substrate 930so as to face the displacement electrodes 951 to 955.

This acceleration detector 900 has the following merits. First, sincethe working portion 911 performs the function as the weight body, thestructure is simple. Further, since the working portion 911 canconstitute a relatively large block, a sufficient mass is provided, thusmaking it possible to improve the sensitivity. Furthermore, since fivedisplacement electrodes 951 to 955 are all formed on the upper surfaceof the working portion 911, displacement can be sufficiently produced bythe action of an acceleration. Thus, sensitivity can be improved.Further, since L shaped through holes 961 to 964 are provided so as tosupport the working portion 911 by the flexible portion 912 in a beamform, the sensitivity is further improved. In addition, the flexiblesubstrate 910 of such a structure can be easily processed by the processsuch as etching, etc. It is to be noted, in order to further improve thesensitivity, it is sufficient to provide a weight body 941 and apedestal 942 which can be constituted by cutting a single substrate 940,as shown in FIG. 44, between the flexible substrate 910 and the controlsubstrate 920.

What is claimed is:
 1. An acceleration sensor using a piezoelectricelement comprising:a sensor casing; a fixed substrate fixed on thesensor casing; a displacement substrate facing the fixed substrate; aworking body fixed to the displacement substrate, said working bodytransmitting a force produced on the basis of an acceleration appliedthereto to the displacement substrate to cause a displacement; a fixedelectrode formed on a surface, which faces to said displacementsubstrate, of said fixed substrate; a displacement electrode formed on asurface, which faces to said fixed substrate, of said displacementsubstrate; and a piezo electric element formed in a manner that it isput between said fixed electrode and said displacement electrode totransform an applied pressure to an electric signal, said electricsignal being outputted from said electrodes; wherein any one or both ofsaid fixed electrode and said displacement electrode are constituted bytwo localized electrodes to form two detection elements by using saidtwo localized electrodes, respectively, a first localized electrode toform a first detection element being located in a positive area withrespect to a first axis of coordinates, a second localized electrode toform a second detection element being located in a negative area withrespect to said first axis, said first axis and a second axis beingperpendicular to each other on a surface where said localized electrodesare formed; an acceleration component in said first axis direction beingdetected by a difference between electric signal values outputted fromsaid first and second detection elements; an acceleration component in athird axis direction perpendicular to said first axis and said secondaxis being detected by a sum of electric signal values outputted fromsaid first and second detection elements.
 2. An acceleration sensorusing a piezoelectric element comprising:a sensor casing; a fixedsubstrate fixed on the sensor casing; a displacement substrate facingthe fixed substrate; a working body fixed to the displacement substrate,said working body transmitting a force produced on the basis of anacceleration applied thereto to the displacement substrate to cause adisplacement; a fixed electrode formed on a surface, which faces to saiddisplacement substrate, of said fixed substrate; a displacementelectrode formed on a surface, which faces to said fixed substrate, ofsaid displacement substrate; and a piezo electric element formed in amanner that it is put between said fixed electrode and said displacementelectrode to transform an applied pressure to an electric signal, saidelectric signal being outputted from said electrodes; wherein any one orboth of said fixed electrode and said displacement electrode areconstituted by four localized electrodes to form four detection elementsby using said four localized electrodes, respectively, a first localizedelectrode to form a first detection element being located in a positivearea with respect to a first axis of coordinates, a second localizedelectrode to form a second detection element being located in a negativearea with respect to said first axis, a third localized electrode toform a third detection element being located in a positive area withrespect to a second axis of coordinates, a fourth localized electrode toform a fourth detection element being located in a negative area withrespect to said second axis, said first axis and said second axis beingperpendicular to each other on a surface where said localized electrodesare formed; an acceleration component in said first axis direction beingdetected by a difference between electric signal values outputted fromsaid first and second detection elements; an acceleration component insaid second axis direction being detected by a difference betweenelectric signal values outputted from said third and fourth detectionelements.
 3. An acceleration sensor using a piezoelectric element as setforth in claim 2:wherein an acceleration component in a third axisdirection perpendicular to the first axis and the second axis isdetected by a sum of electric signal values outputted from said first tofourth detection elements.
 4. An acceleration sensor using apiezoelectric element comprising:a sensor casing; a fixed substratefixed on the sensor casing; a displacement substrate facing the fixedsubstrate; a working body fixed to the displacement substrate, saidworking body transmitting a force produced on the basis of anacceleration applied thereto to the displacement substrate to cause adisplacement; a fixed electrode formed on a surface, which faces to saiddisplacement substrate, of said fixed substrate; a displacementelectrode formed on a surface, which faces to said fixed substrate, ofsaid displacement substrate; and a piezo electric element formed in amanner that it is put between said fixed electrode and said displacementelectrode to transform an applied pressure to an electric signal, saidelectric signal being outputted from said electrodes; wherein any one orboth of said fixed electrode and said displacement electrode areconstituted by five localized electrodes to form five detection elementsby using said five localized electrodes, respectively, a first localizedelectrode to form a first detection element being located in a positivearea with respect to a first axis of coordinates, a second localizedelectrode to form a second detection element being located in a negativearea with respect to said first axis, a third localized electrode toform a third detection element being located in a positive area withrespect to a second axis of coordinates, a fourth localized electrode toform a fourth detection element being located in a negative area withrespect to said second axis, said first axis and said second axis beingperpendicular to each other on a surface where said localized electrodesare formed, a fifth localized electrode to form a fifth detectionelement being located on the surface containing said first axis and saidsecond axis, said fifth localized electrode having a substantiallysymmetrical shape with respect to an intersecting point of said firstaxis and said second axis; an acceleration component in said first axisdirection being detected by a difference between electric signal valuesoutputted from said first and second detection elements; an accelerationcomponent in said second axis direction being detected by a differencebetween electric signal values outputted from said third and fourthdetection elements; an acceleration component in a third axis directionperpendicular to said first axis and said second axis being detected byan electric signal value outputted from said fifth detection element.